Many electric control units (ECUs) which handle various control of information systems such as a navigation system and an audio system, power-train systems such as an engine and a chassis, and body systems such as an air conditioner, headlights, and doorlocks, are mounted in a vehicle.
For example, CAN is widely used as a protocol of a communication network which connects these ECUs. The ECUs mounted in a vehicle can be divided into the ECUs which are always executing control of, for example, engine, brake, and airbag, and the ECUs which are required to be operated only when events such as opening/closing of a sunroof occurs. Meanwhile, CAN has the specifications in which all the ECUs become the ON-state after the engine is started or the electric power is supplied in the vehicle.
As data transmission techniques in this type of communication network, for example, the technique which use a CAN bus for storing data or carrying out diagnosis without using the CAN protocol (see Japanese Patent Application Laid-Open Publication No. 2004-535742 (Patent Document 1)) and the technique which enable data communication by a universal asynchronous receiver transmitter (UART) regardless of the communication protocol of a wired LAN (see Japanese Patent Application Laid-Open Publication No. 2006-020038 (Patent Document 2)) are known.